The present invention relates in general to yarn tensioning apparatus for tensioning a running length of yarn, such as textile yarn or industrial yarn, or the like, and more particularly to yarn tension control apparatus of the ball and funnel type particularly suitable for tension control of textile yarn which is electronically controlled to exert electromagnetic tensioning forces on the yarn from a control capable of governing large groups of the units to hold a selected tension value.
There is a widespread dependence of overall quality in most textile processing on the precision or uniformity of tension of the individual yarn ends. Once yarn tension control is lost or allowed to vary at any point of the process, whether winding, beaming, texturizing, knitting or other fabric formations, the quality degeneration is difficult or impossible to compensate for. Streaking, barre, off yield, excessive knitting defects, denier variation, are familiar problems that frequently have their origin in incorrect or uncontrolled tension of the individual yarn ends.
Probably the most common type of tension device in current use is the post and disc type tensioner wherein the yarn is routed around circular posts to generate friction and build tension. The advantage of this type tensioner is its simplicity and low cost, but it has a significant disadvantage in that the tension developed by the wrapping depends on how much tension is in the yarn as it approaches the wrapped post. Since the tension in the yarn leaving such a tensioner is equal to the tension from the yarn source times a constant K determined by the wrap angle or number of posts, and the tension of the yarn going into the post and disc unit is usually uncontrolled, multiplying the supply or feed yarn tension by some factor simply makes the tension larger but still uncontrolled. For example, considering a common example involving pulling yarn from packages for warping, the supply or feed yarn tension to the post and disc tensioners may vary from 1/2 gram for a full package fed at 100 yards/min. as the beamer is coming up to speed after a stop to remove a slub, to 1 gram for the full package at a full beamer running speed of 500 yards/min. to 3 grams when the package is almost empty at full beamer running speed. If these variations are applied to a post and disc type tensioner which multiplies tension by some value, such as 5, then the yarn tension to the beamer would vary between 21/2 and 15 grams, producing a 6 to 1 variation in tension which can cause streaks in finishing, defects in knitting, etc.
An object of the present invention, therefore, is the provision of a novel yarn tensioner apparatus of the controlled additive type which can be electronically commanded to add a certain tension value to the yarn being fed therethrough and thereby minimize the effects of uncontrolled input tension.
Another object of the present invention is the provision of a novel ball and funnel type yarn tension device having an electromagnet coil for applying tension adding magnetic forces to the ball or balls therein and wherein a plurality of such devices forming a channel are controlled by electronic circuitry which enables the tension value added to the yarn fed through the tension devices of such channel to be readily adjusted by a tension setting potentiometer to different desired values and which provides highly accurate tension control over a wide range of textile yarn tensions.
Another object of the present invention is the provision of yarn tension apparatus of the type described in the immediately preceding paragraph, wherein a plurality of the tension devices form a controlled channel and the electronic circuitry for controlling the electromagnet coils of the tension devices of such channel includes a reset circuit including degaussing circuit means for applying intermittent negative-going reset pulses to the electromagnet coil during periods when the tension setting potentiometer is being adjusted causing changes in the control voltage applied to the coils to vary tension adding values, and thus minimize residual magnetic effects during reduction in the control voltage level.
Another object of the present invention is the provision of a novel ball and funnel type yarn tension apparatus as described in the immediately preceding paragraph, wherein a flag or graduated light mask on a pivoted arm is positioned by the yarn leaving the tension devices to indicate the tension value of the leaving yarn and light sensing means and associated circuitry is provided to vary magnetic forces applied to the ball or balls to enable the leaving tension value to be maintained at a substantially constant level.
Other objects, advantages and capabilities of the present invention will become apparent from the following detail description, taken in conjunction with the accompanying drawings showing preferred embodiments of the invention.